The present invention relates to controlling access to digital signals distributed via a cable television ("CATV") network or the like, and more particularly to a method and apparatus for reencrypting digital signals received from a first communication path (e.g. satellite) prior to retransmission along a second path such as a CATV network. The reencrytion is used to control subscriber access to services provided via the second path, such as digital video and audio services, audio only services, data services and the like.
In cable television networks, subscribers are connected to a transmission stream carrying, e.g., television programs, radio programs, and associated data which originates at a headend. To generate the transmission stream, the headend receives signals from a variety of sources including, for example, broadcast stations, data sources and premium channels via satellite. The signals are combined at the headend into various packages for retransmission to subscribers over the CATV network.
The CATV network may, e.g., be configured as a ring network, star or a tree and branch type structure which extends from the headend to feed various authorized subscribers. Subscribers may be arranged into groups based upon an attribute such as type of programming services required. For example, a subscriber such as a hospital requires a particular type of CATV service, i.e., a package including such services as data service channels and pertinent hospital video/audio channels as opposed to a residential subscriber which may require a package including family oriented channels.
Presently, to retain control and authorize access to various subscriber groups, the headend receives the various signals and, where received in an encrypted format, decrypts and retransmits the signal in a conventional scrambled analog format to provide security for premium channels, thereby preventing unauthorized use. Converters and descramblers located at the subscriber's residence or business are connected to receive and descramble the transmitted analog signal for end use. Encryption schemes for use in digital access control are well known, as evidenced by U.S. Pat. No. 4,613,901 to Gilhousen et al., which discloses a system and method for encrypting and selectively decrypting television signals. An example of an analog scrambling system useful in CATV systems can be found in U.S. Pat. No. 4,222,068 to Thompson.
Unfortunately, pirating of the signal transmitted from the headend cannot be prevented. A large market for pirate descramblers and the like is ready made by the large number of possible end users, thus making it very profitable to breach the security placed on the transmission at or before the headend. This problem is particularly acute in a digital transmission system, where the use of the same encryption scheme along the entire path from a programmer to an end user (e.g., via satellite and cable communication paths) would enable a security breach to have far reaching effects. Therefore, it would be advantageous to provide a method and apparatus for segmenting the network (e.g., between the satellite and CATV systems or between different CATV systems) to minimize the impact of a security breach. It would be further advantageous to provide a security scheme for the transmission of digital television signals over a cable television network. While past CATV systems have been primarily analog, the development of digital video compression and transmission techniques has made digital television a reality. Yet another advantage would be to decrypt and reencrypt a signal without decompressing the data, video and/or audio information being transmitted. Digital audio services via a CATV network have also been introduced, further increasing the demand for effective security schemes.
In segmenting a communication network, several additional advantages including increased control over billing, tiering, pricing, and service packaging throughout the network are realized. For example, in the situation where a CATV network extends throughout more than one town or city, different pricing for services and different service packages may have been contracted for or otherwise be desirable in different towns. Moreover, different subscriber groups, such as businesses and residences would require different service packages, as previously described, and a segmented network would provide additional control over service packaging for various portions of the network. The reliable provision of access control for such needs must be achieved in order to bring these features to the marketplace.
The present invention provides a method and apparatus for communicating encrypted digital signals over a network having the aforementioned features and advantages.